1. Field of the Invention
The present invention relates to an apparatus for expressing relationship of a document group having a hyperlink structure in a tree structure, and a method therefor.
2. Description of the Related Art
A document group on the World Wide Web (WWW) forms a hypertext structure (which is also referred to as a hyperlink structure) with documents as nodes and links among the documents as arcs. The hypertext structure has such an advantage that arbitrary documents can be easily connected by links, but in the case where the number of documents is increased to complicate the relationship among the document, the relationship among the documents is difficult to be comprehended by humans since it is basically a network structure.
Under the circumstances, method for simplify the hypertext structure to display in a tree structure has been used. Examples of the method include a method described in JP-A-6-35657. In this method, in the case where a hypertext structure having plural nodes linked to one node (which is assumed as node A) is converted to a tree structure, one of the plural nodes is selected, and the node A is disposed as a child of the selected node, reference nodes for showing the node A are disposed as children for the other nodes linked to the node A. In this process, upon following the links of the hypertext structure, the link root node upon firstly reaching the node A is designated as a parent of the real node A on the tree structure. The reference nodes are displayed in a different manner from the real nodes constituting the tree structure. The reference nodes indicate the same document as the real node A, but the relationship on the tree structure is shown by the real node A as the representative. Therefore, the reference node has no child node.
JP-A-2002-288225 also describes an apparatus for displaying a hypertext structure in a tree structure.
The web site management tool “GoLive”, produced by Adobe Systems, Inc., has such a function that upon designating a starting document on WWW, the hypertext structure is inspected by sequentially following the links from the document, and upon designating one document in the hypertext structure, a tree structure is formed and displayed based on the hypertext structure with the selected document as a root node.
In the case where a hypertext structure is converted and displayed in a tree structure by these conventional methods, the sequence of following the links of the hypertext structure determines the position of a certain document on the tree structure, i.e., which the plural nodes on the hypertext structure become a child of the node. Accordingly, the position of the document on the tree structure may change by changing a link description of another document even though the document itself is not changed. In the case where the position of the real node is changed on the tree structure, the positions of all the nodes in the sub-tree extending from the real node are changed. Therefore, there is such a problem that even in the case where a user memorizes a position of a certain document on a tree structure and thereafter attempt to access the document, it becomes difficult to explore the document because the position of the document on the tree structure is changed.
Furthermore, because hypertext links can be freely configured, a tree structure formed from a hypertext structure has no direct relationship to the conceptual classification of the documents constituting the hypertext structure. Therefore, even in the case where, for example, the relationship of documents in a web site is displayed in a tree structure formed from the hypertext structure, it cannot be always such an expression that is intelligible and memorable to a user. For example, a top page of a web site has links to miscellaneous renewal information in addition to index pages of subordinate classes, and in the case where it is simply expressed in a tree structure, the index pages and the renewal information pages, which have different concepts, are equally displayed, which is not intelligible to a user.